PROJECT SUMMARY/ABSTRACT The most significant advance in the treatment of Myocardial Infarction (MI) has been reperfusion therapy, which must be applied immediately after the MI diagnosis has been made. Despite the thousands of studies on drug therapies designed to reduce the size of the MI, most have failed in clinical trials. Our hypothesis is that a major reason why these drugs failed is that they must be administered before therapeutic cardiac catheterization is performed. This significantly limits their utility in the clinical setting. The current proposal is based on studies in the Adenylyl Cyclase type 5 (AC5) knock out mouse model, which is protected against myocardial ischemia, obesity, diabetes and has enhanced exercise capacity and lives longer than wild type. Our preliminary data demonstrate that pharmacological inhibitors of the AC5 enzyme have a unique advantage in that they reduce infarct size even when administered after coronary reperfusion. We have developed a novel, more potent and more selective AC5 inhibitor, C90, which is particularly attractive because it is a potent non-nucleoside adenine AC5 inhibitor and also is not toxic. We have a patent pending on C90 and selected this compound for clinical development based on efficacy, pharmacology and safety. Preliminary data indicate that C90 can reduce infarct size when administered after reperfusion by more than 50% in a mouse MI model. The goal of this proposal is to obtain proof-of-principle in mice, in Watanabe rabbits with atherosclerosis and in a large mammalian animal model for infarct size, cardiac function and complete IND-enabling pharmacology, ADME and toxicology studies.